Our laboratory and others are focused on investigating the cellular and molecular mechanisms of virally- induced demyelination to provide a better understanding of how viral infections promote the onset and progression of the human neuroinflammatory disease, multiple sclerosis (MS). This study will examine the innate and adaptive immune functions of central nervous system (CNS)-resident cells, microglia, in a virally- induced murine model of MS, Theiler's murine encephalomyelitis virus-induced demyelinating disease (TMEV-IDD). To achieve this goal, these studies will investigate the function of innate immune molecules to promote immune responses of microglia in virus infections. Since, both TLR3 and PKR (pattern recognition receptors-PRRs) recognize viral double-stranded RNA, these molecules are most relevant for sensing viruses. Therefore, we will focus on deciphering the functions of these PRRs in CMS viral infection. In Specific Aim 1, in the absence of CNS-specific TLR3 and PKR expression, microglia will be assessed to initiate innate immune (cytokine/chemokine secretion and phagocytosis) responses to virus infection. Disease onset and progression will also be evaluated in the absence of PRR expression. These experiments will reveal if expression of these molecules are critical for microglial activation in response to a viral infection and if CNS-restricted expression is required for inhibition of disease onset and progression. In the absence of TLR3 or PKR expression in the CNS, it is expected that disease onset and innate immune activation of microglia will be reduced. In Specific Aim 2, with the presence or absence of TLR3 or PKR in the CNS, microglia will be examined for their functional ability to enhance antigen presentation (co- stimulation and major histocompatibility complex expression &T lymphocyte activation and proliferation) properties at distinct (anti-viral and anti-myelin) phases of TMEV-IDD using in vitro and flow cytometric techniques. These findings will provide information about how the expression of TLR3 and PKR in the CNS promotes the activation of microglial-antigen presentation abilites. Together, these proposed experiments will advance our knowledge of the immune functions of microglia in CNS viral infections. These proposed experiments will contribute to a better understanding of how microglia initiate immune responses during CNS viral infections. With an improved understanding of how these cells contribute to virally-induced disease onset and progression, we can develop novel therapeutic strageties targeting microglia for treatments in neurodegenerative and CNS inflammatory diseases.